The present invention relates to a special chromatographic sheet and a system of chromatographic sheets. The chromatographic sheet or the system of chromatographic sheets of the invention enables the user to develop several chromatograms simultaneously by overpressured layer chromatographic technique.
Late years the liquid chromatography techniques of planar as well as coloumn arrangement have undergone a speedy development. The coloumn-arranged, high-performance liquid chromatography (HPLC) (see J. J. Kirkland /ed./: Modern Practice of Liquid Chromatography, Wiley, N.Y., 1971) and the so-called high-performance thin-layer chromatography (HPTLC) (see W. Bertsch, S. Hara, R. E. Kaiser and A. Zlatkis: Instrumental HPTLC, Huthig, Heidelberg, 1980) were developed. The most important features of this latter one are the use of adsorbents comprising fine particles and a high degree of instrumentation. The fact, that effective separation can be achieved only on fine-particle sorbent layers indicates the restricted applicability of the technique of HPTLC, as good resolution is provided only in shorter distances. It was reasonable to develop a technique which is on the one hand similar to the coloumn chromatographic technique from the point of view of the well-standardizable conditions, on the other hand possesses with the essential advantages of the thin-layer chromatographic (TLC) technique (the possibility of visual evaluation, the possibility for using aggressive agents, the maplike identification).
These requirements are satisfied by a technique what is called overpressured layer chromatography (OPLC) which unifies the advantages of HPLC, HPTLC and the classical TLC. The essential apparatus of this technique is the pressurized ultramicro chamber in which the sorbent layer (e.g. silica gel, talcum, etc.) is completely covered preferably with a flexible membrane and this membrane is pressed in a cushion-like manner against the sorbent layer, thus the vapour space over the layer is eliminated. The micropump charging the eluent passes the eluent into the sorbent layer with an adjustable forced flow (see Hungarian Patent specification No. 173,749; British patent specification No. 1,570,760). There is possibility for linear development in one or two directions, as well as circular and triangular (anticircular) development by changing the place and shape of the eluent inlet.
The main advantage of OPLC are over TLC and the modern HPTLC:
the development can be carried out in a shorter time, PA1 due to the quicker development the diffusion is less, the spots and bands are smaller, the number of theoretical plates increases, PA1 the development can be carried out even by viscous eluent mixtures or which badly wet the sorbent layer, and which chromatogram could not or could hardly be developed by conventional means. PA1 one or several channels leading the eluent can be cut into the sorbent layer, PA1 one or several channels or edges leading the eluent can be made on the sheet working in a cushion-like manner, PA1 the perforation is made at right angles to the direction of the migration of the eluent and its shape is a longitudinal slit, PA1 each sorbent layer can be covered by a perforated sheet supplied with leading channel or edge.
In order to achieve a linear chromatogram by the aid of OPLC where the components are effectively separated, the edges of sorbent layers being on the chromatographic sheets must be suitably sealed by removing the sorbent from the edges of the layer, closing them with a sealent and covering them with an elastic foil. Thus the eluent cannot escape due to overpressure. But that is not enough for providing an effective separation. The travelling of the eluent with a linear front can be assured by the formation of a channel adjoining the eluent inlet.
This problem is solved by a flexible, replacable sheet (plate) protecting the cushion, too which is superposed to the sorbent layer. On the sheet (gap block) one or several channels are formed next to the eluent inlet on the side connecting to the sorbent layer.
By this time in the apparatuses of the over-pressured layer chromatographic techniques only one chromatographic sheet could be developed, though the efficiency of this techniques could be significantly increased if more than one chromatographic sheet were able to be developed simultaneously. The technique of OPLC as the classical technique of TLC gives a preferable possibility to use different specific colour reactions, but when a large number of samples has to be compared, each chromatographic sheet has to be developed separately, which takes a long time and a great place. The OPLC also needs the use of chromatographic sheets with different sorbent layers, but in order to choose the suitable eluent a great number of experiments has to be carried out.